Coastal evolution on Earth and Titan

Abstract

The morphology of a shoreline can provide insight into the processes that have modified the coast. This thesis investigates how coastal processes can leave fingerprints on the morphology of a coast in sandy environments (barrier islands) and detachment-limited environments (rocky coasts of Earth and possibly Titan). Barrier islands are dynamic and ephemeral, facing an uncertain future from climate change and anthropogenic redistribution of sediment. To evaluate barrier resilience to sea-level rise, I propose a novel dimensionless metric called the Washover Ratio which compares cross-shore (overwash) and alongshore transport. Using this ratio, I find that decreases in overwash flux within the narrow middle section—possibly representing the effects of development—lead to a diminished response to sea-level rise across the entire barrier, and therefore a more vulnerable barrier overall. Further investigation of the balance between overwash and alongshore sediment transport allows for an evaluation of barrier island stability to overwash-induced breaching, which is applied to barriers in the Gulf of Mexico. Beyond Earth, Titan, Saturn’s largest moon, is home to the only other active coastlines in our solar system. However, data is sparse for this icy moon. I investigate the signatures of coastal processes found in the planform shape of its coasts using a combination of landscape evolution models and measurements of shoreline shape. Results show that the coastlines of Titan’s seas are consistent with those of both modelled and Earth lakes with flooded river valleys that have been subsequently eroded by waves, particularly when waves saturate (no longer grow in height) at scales up to 10s of km.